It may be a bug in TinyMCE or there may be a configuration setting that would change it, but I don’t know of one.
It’s why many of us work in raw HTML rather than using a Rich Text Editor (TinyMCE in your case).
If you color a paragraph in TinyMCE, and then turn off the RTE (uncheck the Rich Text box on the "Page Settings" tab and save), you should be able to find the tags that turn the color on and off at the beginning and end of the paragraph. Note the color code (something like: #e42a1a;). Highlight the color style (style="color: #e42a1a;"), cut it, and copy it into a span tag around the word:
<span style="color: #e42a1a;">ColoredWord</span>
If there’s a name for the color you want, you can do it this way and skip the step above:
<span style="color:red">ColoredWord</span>
You could also highlight the word’s background like this:
<span style="background-color:blue">Word</span>
You’ll want to leave a space before and after the span.
If you have trouble, turn off the RTE and paste the paragraph code with all the tags into a reply here and we’ll show you what you need to do.
If you’re going to do any significant amount of work on web sites, it’s really worth learning HTML and CSS so you can get things the way you want them without trusting a Rich Text Editor to do the right thing.
BTW, the correct way to do this is to use CSS. In that case, you’d have this
<span class="highlightword">ColoredWord</span>
Then in your CSS file, you’d have:
.highlightword {
color: red
}
That way, you could change the color, background color, size, font weight, and/or font of all the highlighted words on your web site just by changing that section of the CSS file.